Investigation has been vigorously conducted on the use of an organic electroluminescence (EL) device as a display device for color display that replaces liquid crystal in recent years. However, the performance of the organic EL device as a light emitting device is still insufficient to realize the enlargement of the screen size of a display device using the organic EL device. A green light emitting device using an ortho-metallized iridium complex (fac-tris(2-phenylpyridine)iridium), which is a phosphorescent material, as a light emitting material has been proposed as means for improving the performance of the organic EL device (Non-patent Document 1; Non-patent Document 2).
At present, the color of light emitted from an organic EL device utilizing phosphorescence (in other words, a phosphorescent EL device) has been limited to a green color, so the scope of application of the device as a color display is narrow, and the development of a device with improved light emitting property for any other color has been demanded. In particular, no blue light emitting device having an outer quantum yield in excess of 5% has been reported. If the blue light emitting device can be improved, a color display composed only of phosphorescent organic EL devices will be able to display full colors and a white color. Accordingly, the improvement makes great strides forward in putting a phosphorescent EL device to practical use.
At present, the development of a compound containing Ir as a phosphorescent complex has been vigorously conducted, and the following compound A has been known as a compound for a green light emitting device. On the other hand, the following compound B has been known as a compound for a blue light emitting device, but is not practical in terms of the lifetime and efficiency of a device formed of the compound. In view of the foregoing, there arises a need for developing another complex for a blue light emitting device. However, no factor other than the compound B capable of turning the color of light into a blue color has been found at present.

The above-mentioned compounds belong to the group of complexes each using a bidentate chelate ligand. However, few complex using a tridentate chelate ligand similar to the bidentate ligand has been known, and only a compound C (Non-patent Document 3) and a compound D (Non-patent Document 4) shown below, and a few other examples have been known. However, the wavelength of light emission of each of those compounds is in a region of 585 to 600 nm, that is, a red color region, not in a blue color region. If a complex capable of emitting light in a blue color region can be realized by using the new tridentate ligand group, the realization will lead to the possibility of new technical development.

[Non-patent Document 1] D. F. O'Brien and M. A. Baldo et al. “Improved energy transfer in electrophosphorescent devices” Applied Physics letters Vol. 74 No. 3, pp 442-444, Jan. 18, 1999
[Non-patent Document 2] M. A. Baldo et al. “Very high-efficiency green organic light-emitting devices based on electrophosphorescence” Applied Physics letters Vol. 75 No. 1, pp 4-6, Jul. 5, 1999
[Non-patent Document 3] J-P. Collin et al. J. Am. Chem. Soc., 121, 5009 (1999)
[Non-patent Document 4] J. A. G. Williams, Inorg. Chem., 43, 6513 (2004)